Which Arrow Build?

[MattB]

Have you verified the 530 gr "tipping point" with a chronograph, or is that number based on calculations? I haven't found an arrow weight at which KE begins to decrease in all the testing I've done. For example, below is KE vs. arrow weight data I collected a few years ago before and after swapping cams on a Mathews Heli-m I had recently purchased. At the time, I only took arrow weight to ≈500 gr, but I later did additional testing up to 650 gr and KE kept increasing.

An arrow's KE comes from the potential energy developed in the bow during the draw cycle and transferred to the arrow during the shot. A bow's PE is a function of draw weight, draw length, brace height, cam profile, and let-off percentage, and PE remains fixed as long as those parameters aren't changed. With modern compound bows, ≈90% of the PE developed gets transferred to the arrow. The other 10% is "lost" to friction in moving components, acceleration of the string and accessories, continued movement of the string after the arrow decouples, and vibration of the limbs/riser. These losses are perceived as noise and "hand shock." The amount of PE developed in the bow is fixed, but energy losses decrease with increasing arrow weight; thus, a heavier arrow receives more energy from the bow than a lighter arrow (and the bow tends to be quieter with less post-shot vibration). The KE increase is relatively small though, and for practical purposes, KE can be assumed to remain constant.

I've heard it claimed that there is a point somewhere in the multi-thousand grain realm at which arrow KE will decrease due to the bow beginning to "recoil" against the arrow during the shot. I can't confirm that claim, but it sounds reasonable. All my testing has indicated that for realistic hunting/target weight arrows, KE increases (slightly) with arrow weight.
View attachment 163970

Good analysis. Fundamentally, a heavier arrow absorbs more of the bow's energy so KE is higher. The energy the bow creates is either imparted into the bow or dissipated through the bow by vibration. That is why heavier arrows make a bow quieter, more energy in the arrow and less dissipated through the bow/accessories.

 

[Mighty Mouse]

Good analysis. Fundamentally, a heavier arrow absorbs more of the bow's energy so FOC is higher. The energy the bow creates is either imparted into the bow or dissipated through the bow by vibration. That is why heavier arrows make a bow quieter, more energy in the arrow and less dissipated through the bow/accessories.

I think you mean "so KE is higher" (not FOC). But yes, I agree with your summary.

 

[MattB]

I think you mean "so KE is higher" (not FOC). But yes, I agree with your summary.

Yessir, corrected it. In my haste I confused the acronyms that folks spend WAY too much time thinking about but shouldn't.

 

[wildwilderness]

Look, you shoot 72lbs at a 30.5” draw!! Your arrows are going to be heavier than the Average guy shooting 28” at 60lbs.

I see no problem with a 525-550 grain arrow out of your bow.

 

[Greenmachine_1]

Have you verified the 530 gr "tipping point" with a chronograph, or is that number based on calculations? I haven't found an arrow weight at which KE begins to decrease in all the testing I've done. For example, below is KE vs. arrow weight data I collected a few years ago before and after swapping cams on a Mathews Heli-m I had recently purchased. At the time, I only took arrow weight to ≈500 gr, but I later did additional testing up to 650 gr and KE kept increasing.

An arrow's KE comes from the potential energy developed in the bow during the draw cycle and transferred to the arrow during the shot. A bow's PE is a function of draw weight, draw length, brace height, cam profile, and let-off percentage, and PE remains fixed as long as those parameters aren't changed. With modern compound bows, ≈90% of the PE developed gets transferred to the arrow. The other 10% is "lost" to friction in moving components, acceleration of the string and accessories, continued movement of the string after the arrow decouples, and vibration of the limbs/riser. These losses are perceived as noise and "hand shock." The amount of PE developed in the bow is fixed, but energy losses decrease with increasing arrow weight; thus, a heavier arrow receives more energy from the bow than a lighter arrow (and the bow tends to be quieter with less post-shot vibration). The KE increase is relatively small though, and for practical purposes, KE can be assumed to remain constant.

I've heard it claimed that there is a point somewhere in the multi-thousand grain realm at which arrow KE will decrease due to the bow beginning to "recoil" against the arrow during the shot. I can't confirm that claim, but it sounds reasonable. All my testing has indicated that for realistic hunting/target weight arrows, KE increases (slightly) with arrow weight.
View attachment 163970

Love that analysis and testing has proven what that crazy physics teacher was trying to tell us.

Sent from my Pixel 2 XL using Tapatalk

 

[Blockcaver]

If you shoot a skinny shaft (4mm) just run the standard D-6 size insert for weight and stiffening then add an outsert to take a regular 8-32 std thread broadhead (I use Firenocks version). Makes a super durable combination with both the inside and outside of the shaft reinforced near the point. I have not broken an Easton 330 Carbon Injexion using this combination target shooting and hunting, short of when a critter snapped them off on the near side shoulder with the broadhead buried in the far side shoulder. 5 seasons of use with the doubled up insert/outsert combo so far.

 

[nwcurt]

If you shoot a skinny shaft (4mm) just run the standard D-6 size insert for weight and stiffening then add an outsert to take a regular 8-32 std thread broadhead (I use Firenocks version). Makes a super durable combination with both the inside and outside of the shaft reinforced near the point. I have not broken an Easton 330 Carbon Injexion using this combination target shooting and hunting, short of when a critter snapped them off on the near side shoulder with the broadhead buried in the far side shoulder. 5 seasons of use with the doubled up insert/outsert combo so far.

Do you mean something like this (with weights on the back) ?: https://www.lancasterarchery.com/gold-tip-pierce-aluminum-insert.html

Plus this: https://www.lancasterarchery.com/gold-tip-pierce-ballistic-collar.html

 

[Blockcaver]

Do you mean something like this (with weights on the back) ?

Not exactly. Injexions come standard with a stainless steel Deep-6 adaptor (that are small diameter and 6-40 threaded for the special heads) epoxy and push in tool to set them to the right depth. I just put the D-6 insert in to the stock location but it is used only for FOC weight (22 grains if memory is right) and mainly for shaft reinforcing as I don't like nor use D-6 small shanked broadheads.

I then hot melt glue a Firenock outsert over the end of the shaft (34 grains again if memory serves me correctly). Then I use whatever is my favorite standard threaded (8-32 thread) broadhead. Sure been working well for me, and just another option to get decent FOC (16% on my Injexions) and have a durable shaft, broadhead, and adaptor/insert out on the end of the arrow. I happen to like the thin shaft that minimize wind drift and resistance too. I hunt above treeline a fair bit for caribou lately and was seriously hunting sheep when I built the arrows back in 2014. Good luck.